FXUS61 KLWX 270115 AAB
AFDLWX

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
815 PM EST THU NOV 26 2009

.SYNOPSIS...
LOW PRESSURE OFF THE CAROLINA COAST WILL MOVE UP THE EASTERN
SEABOARD TONIGHT...WHILE A COLD FRONT MOVES EAST ACROSS THE MID
ATLANTIC STATES. UPPER LEVEL LOW PRESSURE WILL LINGER INTO
FRIDAY...THEN HIGH PRESSURE BUILDS ACROSS THE AREA THIS WEEKEND.
UNSETTLED CONDITIONS MAY RETURN EARLY NEXT WEEK.

&&

.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
UPDT TO GRIDS/PRODUCTS IN RESPONSE TO PATCHY DENSE FOG
DVLPG...MAINLY E OF I 95 AS SATURATED BOUNDARY LAYER COOLING IN
ADVANCE OF CDFNT. FOG WILL ERODE EWD WITH ONSET OF PRECIP...WHICH
AT 1Z WAS CROSSING THE BLUE RIDGE. OVERALL FCST PLAN AFTER 6Z RMNS
INTACT. TWEAKED HOURLY GRIDS BASED ON LATEST MSAS/OBS...OTHERWISE
NO ADDITIONAL CHANGES. PREVIOUS DISCUSSION FOLLOWS...

RAISED POPS...SPCLY ALONG AND W OF BLUE RIDGE THIS EVE AS BAND OF
SHOWERS MVG INTO WRN ZONES. ADJUSTED HOURLY GRIDS TO REFLECT
CURRENT CONDS...NO OTHER CHANGES ATTM. PREVIOUS DISCUSSION FOLLOWS...

LAST VESTIGES OF THE FOG WERE DISSIPATING EARLY THIS 
AFTERNOON...HOWEVER A STUBBORN STRATUS DECK WAS NOT EASILY ERODING 
ACROSS MOST AREAS EAST OF THE MTNS PER VISIBLE SATELLITE IMAGERY.   

CONTINUE TO BE WATCHING A COUPLE OF SYNOPTIC FEATURES THIS 
AFTERNOON. ONE IS A SURFACE LOW PRESSURE SYSTEM OFF THE CAROLINA 
COAST WHICH WILL MOVE UP THE EASTERN SEABOARD OVERNIGHT. 
MEANWHILE...A STRONG UPPER LEVEL LOW WILL MOVE THROUGH THE GREAT 
LAKES AND SEND A COLD FRONT ACROSS THE MID ATLANTIC REGION TONIGHT. 

MID LEVEL POSITIVE VORTICITY ADVECTION WILL PROMOTE AN INCREASE IN 
SHOWERS LATE THIS AFTERNOON AND EVENING ACROSS THE HIGHLANDS. THIS 
ACTIVITY IS EXPECTED TO HOLD TOGETHER EAST OF THE MTNS DURING THE 
NIGHTTIME HOURS AND HAVE INCREASED POPS ACCORDINGLY. 

IN ADDITION...A WESTERLY WIND BEHIND THE SURFACE COLD FRONT WILL 
START TO ADVECT COLDER TEMPERATURES ACROSS THE HIGHLANDS. THIS 
UPSLOPE FLOW WILL KEEP SHOWERS FLYING AND P-TYPE WILL CHANGE FROM 
RAIN TO SNOW ALONG AND WEST OF THE ALLEGHENY FRONT. SNOW WILL LIKELY 
BEGIN TO ACCUMULATE OVERNIGHT. WINTER STORM WATCH WILL BE CANCELLED 
HOWEVER WILL RAISE A WINTER WEATHER ADVISORY FOR SNOW FOR THE 
WESTERN 5 COUNTIES FOR UPSLOPE SNOWFALL THAT BEGINS OVERNIGHT 
TONIGHT.

&&

.SHORT TERM /6 AM FRIDAY MORNING THROUGH 6 PM FRIDAY/...
UPPER LEVEL LOW PRESSURE WILL BE SLOW TO EXIT ON FRIDAY...AND MODELS 
PROJECT ADDITIONAL VORT ENERGY WRAPPING AROUND THE BASE OF THE 
LOW...SO HAVE CONTINUED SHOWER CHANCES ACROSS MOST OF THE CWA. 
MEANWHILE...SNOW SHOWERS WILL CONTINUE ACROSS FAVORABLE UPSLOPE 
AREAS. WINTER WEATHER ADVISORY CONTINUES FOR 2 TO 4 INCHES OF SNOW
DURING THE DAYTIME HOURS.

IN ADDITION...COLD ADVECTION WILL AID IN MOMENTUM TRANSFER OF A 40+ 
KNOT LOW LEVEL JET MAKING FOR A BLUSTERY/WINDY DAY ACROSS THE ENTIRE 
CWA. WILL HAVE TO WATCH GUSTS OVER THE HIGHER ELEVATIONS FOR 
MARGINAL WIND ADVISORY CRITERIA. HAVE HELD OF ON RAISING WIND 
ADVISORY ATTM.

&&

.LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/...
ONE LAST SHOT OF UPPER ENERGY /A SMALLER SCALE UPPER VORT SLIDING 
AROUND THE SRN END OF THE UPPER LOW/ WILL ROTATE ACROSS THE ERN 
HALF OF THE REGION LATE FRI INTO THE OVERNIGHT HRS. THIS FEATURE 
WILL BASICALLY KEEP WINDS GUSTING WELL INTO THE LATE...INSTEAD OF 
THE GRADUAL DECREASE THAT TYPICALLY OCCURS DURING THE EVNG /AFT 
SUNSET/. WINDS WILL ESPECIALLY STAY GUSTY OVER THE BAY...W/ GALE 
HEADLINES UP WELL INTO THE OVERNIGHT HRS W/ THIS SECONDARY SURGE.

OUTSIDE OF THE BREEZY CONDITIONS...PRECIP IS EXPECTED TO BE WELL 
OFF THE MID ATLC COASTLINE BY LATE FRI EVNG...EXCEPT ACROSS THE 
WRN UPSLOPE REGIONS OF THE CWA. LIGHT ACCUMULATIONS OF SNOW STILL 
EXPECTED INTO THE OVERNIGHT HRS AND THE UPSLOPE MACHINE FROM THE 
EXITING UPPER LOW CONTINUES TO PUSH LAKE EFFECT SNOWS DOWN WRN 
OH/ERN PA FROM LAKE ERIE. BY THE PRE-DAWN HRS SAT...THE MID LEVEL 
GRADIENT WILL WEAKEN AND SUPPORTING LOW LEVEL WIND PATTERNS WILL 
SHIFT TO MORE WLY INTO THE REST OF THE MRNG...ENDING THE UPSLOPE 
SNOW BY LATE MRNG. 

SATURDAY WILL BE A TRANSITION DAY FOR MUCH OF THE CONUS...AS A 
STORM SYSTEM GEARS UP OVER THE DESERT SW. A WEAK UPPER RIDGE WILL 
GIVE THE MID ATLC A QUIET WEEKEND...THO THIS IS JUST AHEAD OF A 
NOTICEABLE REGIME CHANGE THAT WILL GIVE-WAY TO A FAIRLY ACTIVE 
UPCOMING WEEK. 12Z RUNS OF THE GFS/GEM/ECM ALL IN FAIRLY GOOD 
AGREEMENT THAT BOTH THE EARLY WEEK FRONTAL SYSTEM AND LATE WEEK 
LOW ARE A BIT LESS INTENSE THAN PREV RUNS. FIRST...THE DESERT SW 
LOW DOESN/T QUITE PHASE W/ A BROAD POSITIVELY TILTED UPPER TROF 
ACROSS THE NRN ROCKIES. INSTEAD...THE UPPER WAVE CONTINUES DOWN 
INTO THE NRN PLAINS AND GREAT LAKES W/ A WEAK AND DISORGANIZED 
MOISTURE CONVEYOR BELT LINKED DOWN TO THE MEANDERING UPPER LOW 
OVER NRN BAJA. THE DISCONNECT BETWEEN THESE SYSTEMS WILL ALLOW 
THE INITIAL UPPER WAVE TO PUSH THROUGH THE MID ATLC A BIT FASTER 
/LATE MON INTO EARLY TUE/ WITH ONLY SCATTERED PRECIP ALONG THE 
FRONT.

BY THE TIME THE FRONTAL SYSTEM EXITS TO THE SOUTH OF THE MID 
ATLC...THE SW UPPER LOW WILL FINALLY PHASE W/ ANOTHER APPROACHING 
UPPER WAVE OVER THE CANADIAN ROCKIES...PUSH OUT IN THE SRN PLAINS 
BY MID WEEK AND LOOK FOR A POSSIBLE COASTAL LOW TO QUICKLY SLIDE 
UP THE SERN COAST LATE WED INTO THU. A LOT OF THIS STORM SYSTEM/S 
INTENSITY-TRACK WILL DEPEND ON THE STAGNANT LONGWAVE TROF RESIDING 
OVER SOUTH CNTRL CANADA. SEVERAL UPPER VORT LOBES WILL BE SLIDING 
AROUND THE BASE OF THIS FEATURE...AND ANY ONE OF THEM COULD KEEP 
THE SOUTHEAST LOW SUPPRESSED FURTHER SOUTH AND/OR DECREASE THE 
OVERALL INTENSITY AS IT MOVES UP THE I-95 CORRIDOR FROM THE 
CAROLINAS INTO THE MID ATLC.

&&

.AVIATION /01Z FRIDAY THROUGH TUESDAY/...
IFR CONDS AT IAD/MRB XPCD TO LINGER NOW TILL 0Z...THOUGH OVERALL
IMPROVEMENT SHUD BEGIN AS -SHRA MOVE THRU LATER THIS EVNG AND LGT
WLY WINDS ERODE POOR VSBY AND LOWEST STRATUS WITH FROPA. PREVIOUS
DISCUSSION FOLLOWS...

IFR CONDITIONS...MAINLY CIGS...WILL LINGER A LITTLE LONGER UNTIL 
20-21Z...BUT AM EXPECTING AN IMPROVEMENT TO MVFR AT THE HUBS 
THEREAFTER. STRONG SHORTWAVE ENERGY APPROACHES THIS EVENING...LIKELY 
BRINGING SOME SHOWERS SO MVFR CIGS MAY PERSIST TONIGHT AND MVFR 
VSBYS MAY RECUR IN SHRA. GUSTY WEST/NORTHWEST WINDS WILL FILTER IN 
OVERNIGHT INTO FRIDAY BEHIND A SURFACE COLD FRONT.

GUSTY WINDS /20-30KT/ WILL CONTINUE WELL INTO THE OVERNIGHT HRS 
FRI...DECREASING ONLY A BIT FOR THE DAYTIME HRS ON SAT /15-25KT/. 
HIGH PRESSURE WILL THEN QUIET-DOWN WX CONDITIONS ON SUNDAY W/ LIGHT 
WINDS AND NO PRECIP EXPECTED UNTIL LATER IN THE DAY ON MON. A WEAK 
FRONTAL SYSTEM WILL SLIDE THRU LATE MON-EARLY TUE...AND OFF THE 
COAST BY TUE EVNG. ONLY A BRIEF BREAK BEFORE ANOTHER LOW PRESSURE 
SYSTEM BEGINS TO AFFECT THE AREA FROM THE SW...AS A COASTAL LOW 
PRESSURE SYSTEM SLIDE UP TO THE MID ATLC FROM THE DEEP SOUTH REGION 
LATE WED INTO THU.

&&

.MARINE...
MONITORING ONSET OF GUSTY WINDS...APPROACHING BLUE RIDGE AT
1Z...MAY NEED TO BEGIN SCA EARLIER THAN SCHEDULED 7Z. FOG DVLPG
OVER WATERS THIS EVE...WILL UPDATED CWF FOR THIS...NO OTHER
CHANGES ATTM. PREVIOUS DISCUSSION FOLLOWS...

WINDS WILL INCREASE OVERNIGHT TO SMALL CRAFT ADVISORY LEVELS AS A 
COLD FRONT MOVES ACROSS THE WATERS. EXPECT WIND GUSTS TO INCREASE 
WITH DECENT MOMENTUM TRANSFER BY FRIDAY AFTERNOON...AND WILL HAVE 
GALE WARNING IN EFFECT ACROSS THE BAY/LOWER POTOMAC BEGINNING THEN.

GALE CONDITIONS WILL BE LIKELY WELL AFTER SUNSET FRI...POSSIBLY 
INTO THE OVERNIGHT/PRE-DAWN HRS AS ANOTHER UPPER LOW SWINGS DOWN 
OVER THE COASTAL WATERS LATE FRI. SAT WILL STAY BREEZY...MAINLY 
SOLID SCA CONDITIONS THRU THE OVERNIGHT HRS SAT INTO SUN. A WEAK 
COLD FRONT WILL SLIDE THRU EARLY TUE...POSSIBLE PICKING UP WINDS 
BACK INTO LOWER SCA THRESHOLDS. THEN...ONLY ANOTHER ONE-DAY BREAK 
BEFORE ANOTHER LOW PRESSURE /POSSIBLY A COASTAL LOW FROM THE SERN 
COAST/ MOVES TOWARD THE MID ATLC /LATER IN THE WEEK/.

&&

.TIDES/COASTAL FLOODING...
WATER LEVELS REMAIN ABOVE NORMAL...BY A FOOT OR A LITTLE MORE. 
HOWEVER...THESE ANOMALIES ARE NOT EXPECTED TO CAUSE ANY MINOR TIDAL 
FLOODING OVER THE NEXT COUPLE OF HIGH TIDE CYCLES. IN 
ADDITION...ANOMALIES ARE EXPECTED TO DECREASE FRIDAY INTO SATURDAY 
WITH WEST/NORTHWEST WIND BEHIND A FRONT.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...NONE.
MD...WINTER WEATHER ADVISORY FROM 2 AM FRIDAY TO 2 AM EST SATURDAY 
     FOR MDZ501.
VA...WINTER WEATHER ADVISORY FROM 2 AM FRIDAY TO 2 AM EST SATURDAY 
     FOR VAZ021.
WV...WINTER WEATHER ADVISORY FROM 2 AM FRIDAY TO 2 AM EST SATURDAY 
     FOR WVZ054-501-503.
MARINE...SMALL CRAFT ADVISORY FROM 2 AM TO NOON EST FRIDAY FOR 
     ANZ530>534-537>543.
     GALE WARNING FROM NOON FRIDAY TO 6 AM EST SATURDAY FOR 
     ANZ530>534-537>543.
     SMALL CRAFT ADVISORY FROM 2 AM FRIDAY TO 6 AM EST SATURDAY FOR 
     ANZ535-536.

&&

$$
SYNOPSIS...BPP/GMS
NEAR TERM...SBK/BPP
SHORT TERM...BPP
LONG TERM...GMS
AVIATION...SBK/BPP/GMS
MARINE...SBK/BPP/GMS 
TIDES/COASTAL FLOODING...BPP